The present invention relates generally to methods and apparatus for pre-weakening automotive trim covers to provide air bag deployment openings. More specifically, the present invention relates to the elimination of witness marks on trim pieces covering air bag deployment openings.
Air bags are now universally used for the protection of occupants in motor vehicles. Most recently, the use of automotive air bags has expanded to include front and side air bags for both the driver and the front seat passenger. As with many automotive safety features, air bag deployment systems have both utilitarian and aesthetic functionalities which must be addressed. One such feature is deployment access.
As will be known by those skilled in the art, an air bag system has an inflatable cushion housed within a storage compartment, for example behind the instrument panel of the vehicle. The cushion is literally a bag having an inlet that is connected to a gas generator. Upon impact the gas generator rapidly fills the air bag with gas, such that the inflated bag extends outwardly from the storage compartment. The inflated bag then serves as a cushion to help absorb the forward inertial force of the vehicle occupant.
It will be understood by those skilled in the art that air bag enclosures must not impede the expansion of the air bag; that is, in order for the bag to provide protection it must deploy within milliseconds of the initial impact as detected by various vehicle sensors. Thus, no part of the air bag enclosure can be allowed to significantly resist the force of the expanding air bag. Accordingly, some air bag doors are manufactured as separate panels which fit within an opening in the instrument panels and may be hinged along one or several sides. Although they do not interfere with deployment, a line or channel is visible at the intersect of the air bag door and the surrounding instrument panel. In order to provide a more pleasing appearance, alternatives have been sought wherein the instrument panel trim material is an uninterrupted covering which extends over the air bag door substrate pieces; that is, no separate delineation of the air bag door is visible to the vehicle occupants.
One approach which has met with considerable success is the use of laser scoring. In laser scoring, the back of the instrument panel skin is scored to circumscribe the air bag deployment door. In more detail, in one such method a vacuum formed skin is held on a flat plate or fixture. A robotically controlled laser then etches the desired pattern in the skin. It is important that the depth and width of the pre-weakened score line formed by the laser be precisely controlled to ensure that the skin will properly separate or tear when the air bag deploys.
As will be appreciated by those skilled in the art, the instrument panel skin is a polymeric material, typically a thermoplastic which melts under the heat of the laser beam. A portion of the molten plastic is literally vaporized creating a pre-weakened score line. Some of the molten plastic in the pre-weakened line remains briefly molten until it re-solidifies. The drawback to this method occurs when the solidifying plastic in essence shrinks, causing stress that can result in a witness mark on the exterior (visible) surface of the skin when it is removed from the fixture.
It would therefore be desirable to form a true seamless air bag deployment skin, one which does not have a detectable witness mark. The present invention achieves this goal.
In one aspect the present invention provides a method for eliminating laser-induced skin distortion of laser scored skins of the type used to cover air bag enclosures. The method includes the steps of providing a ridge on the skin-retaining fixture immediately beneath the region of the skin to be scored. The ridge functions to lift the skin slightly such that after the skin is scored no distortion of the show surface occurs.
In another aspect the invention provides an apparatus for reducing skin distortions in laser scored skins. The apparatus includes a plate, in one aspect a vacuum plate, for supporting a skin to be scored and a laser mounted above the plate. The plate has a ridge portion which extends slightly above the principal surface of the plate. The ridge is configured to lift a region of the skin immediately beneath the line to be laser scored. The apparatus further includes means for providing relative movement between the laser beam and the plate.
Thus, in its broadest aspect the method of the present invention provides a process for forming an air bag release score line having the steps of placing a layer of laser-scoreable material on a plate; creating a raised region of the material along a predetermined line; scoring the material with a heat source at the raised region of the material; and removing the material from said plate.
In its broadest aspect the apparatus of the present invention includes a plate having a principal surface for receiving a layer of material, the plate having a ridge on its principal surface; a heat source which melts a portion of a thermoplastic skin on the plate; and means for producing relative movement between the heat source and the principal surface of the plate such that a score line of a predetermined depth is formed in the skin along the ridge.